function y=vk(w,i)
Lx=0.1;
Ly=0.2;
Lz=1;
st=0;
c0=344;%sound velocity in air
rand13=mapot(i);
l=rand13(1);
m=rand13(2);
n=rand13(3);
el=1/2;
em=1/2;
en=1/2;
if l==0
    el=1;
end
if m==0;
    em=1;
end
if n==0
    en=1;
end
kiki=pi^2*((l/Lx)^2+(m/Ly)^2+(n/Lz)^2);%ki的平方
y=((w/c0)^2-kiki)*Lx*Ly*Lz*el*em*en;